The impact of flavonoids on spatial memory in rodents: from behaviour to underlying hippocampal mechanisms

Emerging evidence suggests that a group of dietary-derived phytochemicals known as flavonoids are able to induce improvements in memory, learning and cognition. Flavonoids have been shown to modulate critical neuronal signalling pathways involved in processes of memory, and therefore are likely to affect synaptic plasticity and long-term potentiation mechanisms, widely considered to provide a basis for memory. Animal dietary supplementation studies have further shown that flavonoid-rich foods are able to reverse age-related spatial memory and spatial learning impairments. A more accurate understanding of how a particular spatial memory task works and of which aspects of memory and learning can be assessed in each case, are necessary for a correct interpretation of data relating to diet-cognition experiments. Further understanding of how specific behavioural tasks relate to the functioning of hippocampal circuitry during learning processes might be also elucidative of the specific observed memory improvements. The overall goal of this review is to give an overview of how the hippocampal circuitry operates as a memory system during behavioural tasks, which we believe will provide a new insight into the underlying mechanisms of the action of flavonoids on cognition.

Learning and memory in holocaust survivors with posttraumatic stress disorder

Background: Impairments in explicit memory have been observed in Holocaust survivors with posttraumatic stress disorder. Methods: To evaluate which memory components are preferentially affected, the California Verbal Learning Test was administered to Holocaust survivors with (n = 36) and without (n = 26) posttraumatic stress disorder, and subjects not exposed to the Holocaust (n = 40). Results: Posttraumatic stress disorder subjects showed impairments in learning and short-term and delayed retention compared to nonexposed subjects; survivors without posttraumatic stress disorder did not. Impairments in learning, but not retention, were retained after controlling fir intelligence quotient. Older age was associated with poorer learning and memory performance in the posttraumatic stress disorder group only. Conclusions: The most robust impairment observed in posttraumatic stress disorder was in verbal learning, which may be a risk factor for or consequence of chronic posttraumatic stress disorder. The negative association between performance and age may reflect accelerated cognitive decline in posttraumatic stress disorder.

Blueberry-induced changes in spatial working memory correlate with changes in hippocampal CREB phosphorylation and brain-derived neurotrophic factor (BDNF) levels

Phytochemical-rich foods have been shown to be effective at reversing age-related deficits in memory in both animals and humans. We show that a supplementation with a blueberry diet (2% w/w) for 12 weeks improves the performance of aged animals in spatial working memory tasks. This improvement emerged within 3 weeks and persisted for the remainder of the testing period. Memory performance correlated well with the activation of cAMP-response element-binding protein (CREB) and increases in both pro- and mature levels of brain-derived neurotrophic factor (BDNF) in the hippocampus. Changes in CREB and BDNF in aged and blueberry-supplemented animals were accompanied by increases in the phosphorylation state of extracellular signal-related kinase (ERK1/2), rather than that of calcium calmodulin kinase (CaMKII and CaMKIV) or protein kinase A. Furthermore, age and blueberry supplementation were linked to changes in the activation state of Akt, mTOR, and the levels of Arc/Arg3.1 in the hippocampus, suggesting that pathways involved in de novo protein synthesis may be involved. Although causal relationships cannot be made among supplementation, behavior, and biochemical parameters, the measurement of anthocyanins and flavanols in the brain following blueberry supplementation may indicate that changes in spatial working memory in aged animals are linked to the effects of flavonoids on the ERK-CREB-BDNF pathway. (c) 2008 Elsevier Inc. All Fights reserved.

Redintegration and lexicality effects in children: do they depend upon the demands of the memory task?

The effect of long-term knowledge upon performance in short-term memory tasks was examined for children from 5 to 10 years of age. The emergence of a lexicality effect, in which familiar words were recalled more accurately than unfamiliar words, was found to depend upon the nature of the memory task. Lexicality effects were interpreted as reflecting the use of redintegration, or reconstruction processes, in short-term memory. Redintegration increased with age for tasks requiring spoken item recall and decreased with age when position information but not naming was required. In a second experiment, redintegration was found in a recognition task when some of the foils rhymed with the target. Older children were able to profit from a rhyming foil, whereas younger children were confused by it, suggesting that the older children make use of sublexical phonological information in reconstructing the target. It was proposed that redintegrative processes in their mature form support the reconstruction of detailed phonological knowledge of words.

fMRI delineation of working memory for emotional prosody in the brain: commonalities with the lexico-semantic emotion network

Decoding emotional prosody is crucial for successful social interactions, and continuous monitoring of emotional intent via prosody requires working memory. It has been proposed by Ross and others that emotional prosody cognitions in the right hemisphere are organized in an analogous fashion to propositional language functions in the left hemisphere. This study aimed to test the applicability of this model in the context of prefrontal cortex working memory functions. BOLD response data were therefore collected during performance of two emotional working memory tasks by participants undergoing fMRI. In the prosody task, participants identified the emotion conveyed in pre-recorded sentences, and working memory load was manipulated in the style of an N-back task. In the matched lexico-semantic task, participants identified the emotion conveyed by sentence content. Block-design neuroimaging data were analyzed parametrically with SPM5. At first, working memory for emotional prosody appeared to be right-lateralized in the PFC, however, further analyses revealed that it shared much bilateral prefrontal functional neuroanatomy with working memory for lexico-semantic emotion. Supplementary separate analyses of males and females suggested that these language functions were less bilateral in females, but their inclusion did not alter the direction of laterality. It is concluded that Ross et al.'s model is not applicable to prefrontal cortex working memory functions, that evidence that working memory cannot be subdivided in prefrontal cortex according to material type is increased, and that incidental working memory demands may explain the frontal lobe involvement in emotional prosody comprehension as revealed by neuroimaging studies. (c) 2007 Elsevier Inc. All rights reserved.

Conceptual and perceptual processing in prospective remembering

McDaniel, Robinson-Riegler, and Einstein (1998) recently reported findings in support of the proposal that prospective remembering is largely conceptually driven. In each of the three experiments they reported, however, the task in which the prospective memory target was encountered at test had a predominantly conceptual focus, thereby potentially facilitating retrieval of conceptually encoded features of the studied target event. We report two experiments in which we manipulated the dimension (perceptual or conceptual) along which a target event varied between study and test while using a processing task, at both study and test, compatible with the relevant dimension of target change. When the target was encountered in a sentence validity task at study and test, and the semantic context in which a target was encountered was changed between these two occasions, prospective remembering declined (Experiment 1). A similar decline occurred, using a readability rating task, when the perceptual context (font in which the word was printed) was altered (Experiment 2). These results indicate that both perceptual and conceptual processes can support prospective remembering.

False recognition of abstract versus common objects in older and younger adults: testing the semantic categorization account

Older adults often demonstrate higher levels of false recognition than do younger adults. However, in experiments using novel shapes without preexisting semantic representations, this age-related elevation in false recognition was found to be greatly attenuated. Two experiments tested a semantic categorization account of these findings, examining whether older adults show especially heightened false recognition if the stimuli have preexisting semantic representations, such that semantic category information attenuates or truncates the encoding or retrieval of item-specific perceptual information. In Experiment 1, ambiguous shapes were presented with or without disambiguating semantic labels. Older adults showed higher false recognition when labels were present but not when labels were never presented. In Experiment 2, older adults showed higher false recognition for concrete but not abstract objects. The semantic categorization account was supported.

Using what we know: consequences of intentionally retrieving gist versus item-specific information

The effect of a prior gist-based versus item-specific retrieval orientation on recognition of objects and words was examined. Prior item-specific retrieval increased item-specific recognition of episodically related but not previously tested objects relative to both conceptual- and perceptual-gist retrieval. An item-specific retrieval advantage also was found when the stimuli were words (synonyms) rather than objects but not when participants overtly named objects during gist-based recognition testing, which suggests that they did not always label objects under general gist-retrieval instructions. Unlike verbal overshadowing, labeling objects during recognition attenuated (but did not eliminate) test- and interference-related forgetting. A full understanding of how retrieval affects subsequent memory, even for events or facts that are not themselves retrieved, must take into account the specificity with which that retrieval occurs.

Older adults encode-but do not always use-perceptual details: intentional versus unintentional effects of detail on memory judgments

Investigations of memory deficits in older individuals have concentrated on their increased likelihood of forgetting events or details of events that were actually encountered (errors of omission). However mounting evidence demonstrates that normal cognitive aging also is associated with an increased propensity for errors of commission-shown in false alarms or false recognition. The present study examined the origins of this age difference. Older and younger adults each performed three types of memory tasks in which details of encountered items might influence performance. Although older adults showed greater false recognition of related lures on a standard (identical) old/new episodic recognition task, older and younger adults showed parallel effects of detail on repetition priming and meaning-based episodic recognition (decreased priming and decreased meaning-based recognition for different relative to same exemplars). The results suggest that the older adults encoded details but used them less effectively than the younger adults in the recognition context requiring their deliberate, controlled use.

A preliminary investigation of the running digit span as a test of working memory

The objective of this study was to compare performance on different versions of the running span task, and to examine the relationship between task performance and tests of episodic memory and executive function. We found that the average capacity of the running span was approximately 4 digits, and at long sequence lengths, performance was no longer affected by varying the running span window. Both episodic and executive function measures correlated with short and long running spans. suggesting that a simple dissociation between immediate memory and executive processes in short and long running digit span tasks may not be warranted.

Reduced heart rate responding to trauma reliving in trauma survivors with PTSD: correlates and consequences

The authors investigated whether heart rate (HR) responses to voluntary recall of trauma memories (a) are related to posttraumatic stress disorder (PTSD), and (b) predict recovery 6 months later. Sixty-two assault survivors completed a recall task modeled on imaginal reliving in the initial weeks postassault. Possible cognitive modulators of HR responsivity were assessed; dissociation, rumination, trauma memory disorganization. Individuals with PTSD showed a reduced HR response to reliving compared to those without PTSD, but reported greater distress. Notably, higher HR response but not self-reported distress during reliving predicted greater symptom reduction at follow-up in participants with PTSD. Engagement in rumination was the only cognitive factor that predicted lower HR response. The data are in contrast to studies using trauma reminders to trigger memories, which have found greater physiological reactivity in PTSD. The authors' observations are consistent with models of PTSD that highlight differences between cued or stimulus-driven retrieval and intentional trauma recall, and with E B. Foa and M.J. Kozak (1986) hypothesis that full activation of trauma memories facilitates emotional processing.

Posttraumatic stress disorder following assault: the role of cognitive processing, trauma memory, and appraisals

Two studies of assault victims examined the roles of (a) disorganized trauma memories in the development of posttraumatic stress disorder (PTSD), (b) peritraumatic cognitive processing in the development of problematic memories and PTSD, and (c) ongoing dissociation and negative appraisals of memories in maintaining symptomatology. In the cross-sectional study (n = 81), comparisons of current, past, and no-PTSD groups suggested that peritraumatic cognitive processing is related to the development of disorganized memories and PTSD. Ongoing dissociation and negative appraisals served to maintain PTSD symptoms. The prospective study (n = 73) replicated these findings longitudinally. Cognitive and memory assessments completed within 12-weeks postassault predicted 6-month symptoms. Assault severity measures explained 22% of symptom variance; measures of cognitive processing, memory disorganization, and appraisals increased prediction accuracy to 71%.

The intention-superiority effect for naturally occurring activities: the role of intention accessibility in everyday prospective remembering in young and older adults

This study examined age differences in the accessibility of a single pool of naturally occurring intentions both before and after completion. Following Maylor, Darby, and Della Sala (2000), accessibility was measured in terms of the number of activities generated in a 4-minute activity fluency task. Each participant undertook two such tasks. A prospective task in which they generated activities intended for completion during the following week and a retrospective task, I week later, in which they generated activities carried out over the previous week. In a partial replication of Maylor et al.'s findings, young, but not healthy older, adults generated more to-be-completed intentions than completed ones, demonstrating an intention-superiority effect (ISE) for everyday activities. The absence of an ISE for older adults appeared to reflect the reduced accessibility of intentions prior to completion, rather than the impaired inhibition of fulfilled intentions. Moreover, both groups showed greater inaccessibility of completed than intended activities, thus demonstrating an intentioncompletion effect for naturally occurring intentions that is preserved in healthy ageing (cf. Marsh, Hicks, & Bink, 1998). Despite showing a reduced accessibility of intended activities, older adults reported having completed a greater proportion of their intentions during the week than young adults. Moreover, there was a correlation between the ability to access intentions and the proportion of intentions completed only for young adults. These observations suggest that older adults' everyday prospective memory performance may be relatively less dependent on intention accessibility and more dependent on other factors. While there was no age difference in the reported use and effectiveness of external retrieval aids, older adults demonstrated a greater level of temporal organization in the production of their intentions in the fluency task. This is consistent with the possibility that older adults may have more structured daily lives and may be able to use information about the sequence of ongoing events to support superior everyday prospective remembering.